Finite element simulation of mass transfer in laminar swirling decaying flow induced by means of a tangential inlet in an annulus

Abstract

This work is devoted to the numerical modeling of mass transfer on both cylinders of an annular cell subjected to swirling laminar decaying flow induced by means of a single tangential inlet greater in diameter, φ e=12.5 mm , than the annular gap thickness, e=7 mm . The complete diffusion–convection equation has been solved in a three-dimensional frame by means of the FIDAP finite element package using the velocity fields previously predicted by the same numerical technique. As for the flow-field, we have shown that a correct prediction of mass transfer coefficients in such a flow is strongly linked to an adequate mesh generation, especially when mass transfer occurs on the inner wall of the annulus, near which recirculating eddies exist. Numerical results have been found to be in good agreement with experimental data previously obtained on both cylinders of the annulus. A simulation study of the influence of the Schmidt number on the overall mass transfer on the outer cylinder has shown that the mean Sherwood number varies as Sc 0.44. Even for forced convection, the numerical simulation of mass transfer is not directly obtained from the simulation of the dynamics of the flow. Due to the difference in mass and momentum boundary layer thicknesses, the mesh refinement has to be adapted to Schmidt number.